A driver's brake-pedal depression occurring during operation of the automatic brake, gives the driver an uncomfortable feeling that the brake pedal is undesirably forced to move down and thus drawn in, due to a less brake-pedal reaction force or an insufficient reaction force weakened as compared to a normal brake-pedal reaction force.
For the purpose of eliminating such an uncomfortable feeling, an automatic brake device, described in a patent document 1, is configured to produce a brake fluid pressure by actuating an automatic brake means, when it is determined that a great deceleration is required to avoid a collision of a host vehicle with a preceding vehicle ahead of the host vehicle, or when it is determined that, when executing an automatic running mode while maintaining a vehicle-to-vehicle distance to the preceding vehicle at a given distance, the vehicle-to-vehicle distance becomes shorter than the given distance. However, in the presence of a driver's brake-pedal depression during operation of the automatic brake means, a transition from the automatic brake state to the manual brake state occurs. In such a situation, the device is configured to open a cut-off valve when a master-cylinder pressure, produced by the driver's braking operation, and a wheel-cylinder pressure, obtained by the automatic brake, become approximately equal to each other, so as to avoid the occurrence of a poor brake feel that a feel of braking operation is temporarily reduced and an uncomfortable feeling such as a brake-pedal kickback. Patent document 1: Japanese patent provisional publication No. JP8-198075 (A)